Tin-clad substrates for use as current collectors, batteries comprised thereof and methods for preparing same

Abstract

The present invention provides a current collector for a battery which comprises a lead or lead alloy substrate and a thin cladding of tin, batteries utilizing such a current collector and methods for manufacturing such batteries. Preferably the tin cladding is composed of substantially pure tin and the concentration of the tin cladding relative to the weight of the current collector (i.e., the combined weight of the substrate and cladding) is less than 4% by weight. The tin cladding forms a noncontinuous layer over the outer surface of the substrate such that there are interspersed regions of lead and tin at the current collector surface. Batteries utilizing such current collectors exhibit marked improvement in performance compared to similar cells composed of tin alloys. In particular, batteries using current collectors of the present design offer superior cycle life and shelf life performance.

Description

1. The present invention relates to the field of current collectors, electrodes and lead-acid batteries. More particularly, the present invention relates to current collectors composed of a lead or lead alloy substrate and a tin cladding applied to the substrate surface and batteries utilizing such current collectors, such batteries being characterized by both high cycle life and long shelf life. The present invention further relates to methods for manufacturing batteries utilizing this type of current collector.BACKGROUND OF INVENTION2. Despite considerable research into the development of improved electrochemical storage devices, the lead-acid battery remains a predominant device for delivering electrical current in many electrical operations. A conventional lead-acid battery such as the valve-regulated lead-acid (VRLA) battery is comprised of a plurality of cells. Each cell typically includes a set of interleaved monopolar positive and negative electrodes or "plates." The electro...

AI Technical Summary

Benefits of technology

13. The tin cladding enhances shelf life and cycle life performance. The current inventors have found that the key to simultaneously achieving long shelf life and cycle life is to have a semiconducting layer on the outer surface of the current collector. The current collectors provided for in the current invention satisfies this important criterion. Batteries utilizing the tin-clad substrates described herein have superior cycle life and shelf life performance relative to prior art cells. The particular enhancement observed is a function of the tin concentration at the current collector surface. In general, a higher concentration of tin results in particularly high cycle life. At lower tin cladding levels, shelf life performance can be optimized.

Problems solved by technology

Self-discharge not only reduces storage time and discharge capacity but also results in voltage decay, or a decrease in open circuit voltage.

Thus, whether a conductive or passivation layer exists at the current collector / paste interface can dramatically impact the electrochemical properties of a cell.

However, the drawback to a corrosion layer is that the cell generally has reduced shelf life due to the ongoing corrosion or oxidation of the lead or lead alloy current collector which consumes needed electrolyte.

In contrast, current collectors whose composition tends to create passivation layers have excellent shelf life but relatively poor cycle life and recovery from deep discharge and stand.

The extended shelf life is a consequence of the passivation of the corrosion layer which protects the current collector from corrosion and self-discharge and thus voltage decay; yet, as noted above, the passivation process also acts to inhibit current flow during charging, thereby reducing cycle life.

A conductive corrosion layer enhances cycle life but reduces shelf life; a passivation layer, in contrast, negatively affects cycle life but increases shelf life.

It is thought that a relatively high tin content results in the tin being corroded, presumably to soluble tin(II) or insoluble SnO.sub.2.

In particular, the 908 Patent claims that during charging and formation the tin plating can disintegrate to create tin particles that can form deposits at the cathodic plates; these deposits, in turn, can cause a short circuit in the cell.

In general, a higher concentration of tin results in particularly high cycle life.

The thin, substantially non-perforated foil or film is preferred over a grid because the thin, non-perforated foils or films significantly increase the surface area and result in exceptionally high discharge and charge rates.

Images